With the application of low NOx burner technology for reducing NOx emissions in coal-fired boilers in early 1990s, many boilers began experiencing drastic increases in tube wastage rates on the waterwall tubes made of carbon and low alloy steels due to sulfidation attack under low NOx combustion conditions. The early trials and adoption of weld overlays of chromia-forming alloys by the industry in mid- and late-1990s showed surprising successes in eliminating the tube wastage issue for the waterwalls. However, with longer services under the low NOx combustion conditions, some supercritical boilers had experienced circumferential cracking on the waterwall weld overlays. For reheater and superheater applications in coal-fired boilers, weld overlays have also been found to be effective to resist coal-ash corrosion and erosion-corrosion. The current paper reviews the field performance experience for the past two decades of various weld overlay alloys including Fe-Ni-Cr alloys, such as Type 309, Type 312 and alloy 33 (UNS R20033), and Ni-base alloys, such as alloys 625 (UNS N06625), 622 (UNS N06022), 52 (UNS N06052) and 72 (UNS N06072) in both subcritical and supercritical units. Also included in this discussion are two newly developed proprietary Fe-Cr-C hardfacing alloys suitable for weld overlay application to boiler tubes, such as in fluidized-bed boilers, for resisting erosion and abrasive wear.

Subject
Corrosion resistant alloys, Nickel based alloys, Tubes, Welding, Metal wastage, Waterwalls, Reheaters, Erosion, Steel, Boilers, Corrosion protection, Cracking, Alloys
Keywords:
Weld overlay, Stainless steels, Ni-based alloys, Coal-fired boiler, Corrosion/Sulfidation, Circumferential cracking, Coal-ash corrosion, Erosion and abrasive wear
© 2014 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2014
Association for Materials Protection and Performance (AMPP)
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